Fiber optic sensing has been used for probing remote areas that have limited spatial clearance. It is particularly useful in biomedical research for probing internal cavities (e.g., body lumens) and in industrial applications for monitoring hard-to-reach areas such as the inside of a small curved tube. One particular area of fiber optic sensing relates to imaging. A fiber bundle can be used to transmit images coherently along the bundle. This approach is used in endoscopic applications. However, fiber bundles often have a relatively large size, can be stiff and are generally expensive.
Another possible arrangement is to reconstruct an image by scanning a single fiber over a sample of interest. Single-fiber imaging is particularly attractive for certain applications, such as intravascular scanning, because of the small outer diameter of the single fiber. Single-mode fibers are used in applications that require coherent transmission of light, such as low coherence interferometry and optical coherence tomography (OCT). In contrast, multimode fibers are used in applications that do not require coherent transmission of light, but need high collection efficiency, such as fluorescence imaging or Raman spectroscopy.
One technical difficulty of performing single-fiber imaging is the separation of the excitation light and the collection light. Because the excitation light usually is much more intense than collected light, the collected signals are harder to detect relative to the excitation light reflected from various optical interfaces. As a result, it is difficult to obtain real-time color images of the vessel wall in the visible light range using existing optical coherence tomography (OCT) systems. OCT also typically cannot measure light produced by incoherent optic processes such as fluorescence.
A need therefore exists for imaging methods and probes that can provide real-time color images that are suitable for use with an OCT system. The present invention addresses this need and others.